The present invention relates to an improved lubricant composition useful as a processing aid for vinyl chloride polymer compositions.
Lubricants must be employed to improve the flow characteristics and reduce sticking of vinyl chloride polymer compositions processed by extrusion, injection molding, or calendaring. Some of the most commonly employed lubricants include low molecular weight monocarboxylic acids having 8 to 18 carbon atoms, salts of these acids and esters of these acids with aliphatic alcohols having 2 to 24 carbon atoms. Most popular of this category is stearic acid and calcium stearate. Polyethylene having a molecular weight in the range of about 3,000 to 20,000 is taught in U.S. Pat. No. 3,442,837 as a lubricant for polyvinyl chloride (PVC), used either alone or in combination with one of the aforementioned fatty acids or fatty acid derivatives. Furthermore, the use of oxidized polyethylene as a PVC lubricant is taught in U.S. Pat. No. 3,979,347. U.S. Pat. No. 3,862,066 suggests combinations of different lubricants such as paraffin wax and/or calcium stearate blended with oxidized polyethylene.
In some applications lubricant systems containing fatty acids or fatty acid esters are not suitable. For example, the fatty acids and their salts have a tendency to exude from PVC during processing and storage. This is not particularly desirable in those cases where the PVC is extruded into piping materials intended to transport edible liquids or powders, or for packaging applications. It is found that other lubricants such as polyethylene, ethylene polymers containing oxygen, and fatty acid esters require excessive amounts of energy input for extrusion and the PVC does not process easily without the presence of an additional lubricant such as calcium stearate. Increasing the use levels of these lubricants often helps processing, but at the cost of a negative effect on the physical properties of the processed PVC composition. Thus, the skilled compounder often requires a lubricant system which will not exude from the processed resin, will not seriously affect the physical properties of the processed product, will provide good flow properties during processing and will require a minimum amount of extruder energy input thereby allowing for lower processing temperatures and good production rates.
Accordingly, it is an object of this invention to provide a balanced multifunctional lubricant system for heat processing of vinyl chloride polymer compositions.
Another object is to provide a lubricant system for extruded polyvinylchloride which allows the resin to be extruded using less work or input energy and accordingly gives rise to higher production rates.